I'm not sure an SBS is in order for this...I undercoat in burnt umber (or whichever dark brown I grab first). When that is dry on goes the brass...I have a variety of yellow metal paint so I highlight with a lighter shade. An alternative if you have a single paint is to glaze the item with a VERY light coat of dark brown (a glaze is like a wash only you wipe nearly all the paint from the brush before application) and then go back to highlight with the base color. Shadow with darker applications of the brown. This takes a lot longer to describe than to do.--